The present invention relates to industrial polyamide yarns and more particularly relates to very high tenacity polyamide yarn with high modulus and having acceptably low shrinkage and a process for making such yarns.
A wide variety of high tenacity polyamide yarns are known and are used commercially for a variety of purposes. Many of such polyamide yarns are useful in cords for tires and other applications due to high tenacity, i.e., up to but generally not exceeding 10.5 g/d. Such yarns also have tolerable levels of shrinkage for conversion to selected industrial applications such as tire cords, typically 5-10% at 160.degree. C. For most applications in which it is desirable to use a high tenacity yarn, yarns with a higher tenacity than that found in tire yarns would be desirable provided that shrinkage is controlled to low or moderate levels and modulus is kept high.
Low shrinkage yarns with high tenacity levels have been made using processes employing treatment steps such as steaming for relatively long periods after drawing but such processes are usually not well-suited for commercial production. In addition, the yarns made by such processes typically have greatly reduced modulus levels.
A polyamide yarn with a tenacity measured on a yarn basis of greater than about 11 g/d with an acceptable level of shrinkage and high modulus would be highly desirable for many industrial applications, particularly with other desirable properties including high sonic modulus and birefringence. Such yarns would be even more desirable if the yarns were readily manufactured in a commercially-feasible process.